For pine to be toxic one really has to be exposed to the dust, so yes pine boards should be safe.
However, pine boards are a poor choice for cage construction. Most pine boards sold are still fairly moist and can shrink, warp and twist over time as the boards are exposed to climatic changes. Even if dry pine is generally considered to be a very unstable wood, making it a bad choice for the tolerances required is reptile caging.
The laminated pine boards sold at home centers are a bit better but tend to be terribly overpriced for what they are.
Pine is okay as a face frame attached to a more stable cage, but is not good for the entire cage.
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Current snakes:
0.0.1 Gonyosoma oxycephala - Java locale (green)
1.2 Gonyosoma oxycephala - Jave local (green)
2.2 Gonyosoma janseni - Seleyar locale (all black)
1.2 Gonyosoma janseni - Celebes locale (Black & Tan)